As an air belt apparatus, in which a part of webbing of a seat belt apparatus is configured to be an expandable portion, for example, the one described in Japanese Unexamined Patent Application Publication No. 2003-312439 is known.
FIGS. 5 and 6 illustrate the air belt apparatus described in the publication. The seat belt 20 includes a shoulder belt portion 6 and a lap belt portion 7. The shoulder belt portion 6 is withdrawn from a retractor 3 for use in a shoulder belt, which is provided at a lower part of a center pillar 2, and is extended via a through ring 5 provided at an upper part of the center pillar 2. Further, the lap belt portion 7 is withdrawn from a retractor 4 for use in a lap belt, which is provided at a lower part of the retractor 3 for use in the shoulder belt, and is extended via a waist portion of an occupant. At end portions of the shoulder belt portion 6 and the lap belt portion 7, a tongue apparatus 8 is provided. A buckle apparatus 9 with which the aforementioned tongue apparatus 8 is combined is provided by being fixed to a seat base 10 formed of a seat frame (not illustrated) or a slide rail (not illustrated). An inflator 11 for use in an air belt that is integrally provided with the aforementioned buckle apparatus 9 is provided therewith.
The air belt apparatus is configured to be able to softly restrain the occupant by means of that when a vehicle encounters a collision, and an acceleration sensor (not illustrated) for detecting a collision detects a predetermined value or more, a high pressure gas is generated out from the inflator 11 and the high pressure gas intrudes into bags BG1 and BG2 after passing though a gas passageway in the buckle apparatus 9 and a gas passageway in the tongue apparatus 8, and causes the webbings WG1 and WG2 of respective bag-shaped belt portions 6b and 7b of the shoulder belt portion 6 and the lap belt portion 7 to be expanded and developed.
The shoulder belt portion 6 is composed of a normal belt portion 6a that is not in contact with the occupant, and a bag-shaped belt portion 6b serving as the expanding portion. The bag-shaped belt portion 6b having a portion being in contact with a chest portion of the occupant is constructed from the webbing WG1 formed into a bag shape, which generates tension force at a time of the collision of the vehicle. The tension force of the webbing WG1 is generated along with an expansion of the webbing WG1 that is constructed from a circular knitting fabric. The bag BG1 is housed in an inside of the webbing WG1 of the bag-shaped belt portion 6b of the shoulder belt portion 6.
The lap belt portion 7 is composed of a normal belt portion 7a that is not expanded and developed but is in contact with the waist portion of the occupant, and a bag-shaped belt portion 7b having a portion that is in contact with the waist portion of the occupant and is expanded and developed. This bag-shaped belt portion 7b is provided with the webbing WG2 formed into a bag shape, which generates tension force at a time of a collision of a vehicle. The tension force of the webbing WG2 is generated along with an expansion of the webbing WG2 constructed from the circular knitting fabric. The bag BG2 is housed in an inside of the webbing WG2 of the bag-shaped belt portion 7b of the lap belt portion 7.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2003-312439
In a case that the air belt is provided with a bag-shaped belt and a knit cover surrounding the bag-shaped belt, and the knit cover is not practically extended in a longitudinal direction of the air belt, while the same is extendable in an expanding direction of the air belt, and that the length of the knit cover in the longitudinal direction is reduced at a time when the knit cover is expanded, the length of the air belt is entirely reduced along with the expansion of the air belt, and the air belt is brought to fit the occupant.
However, in a case that at least a part of the expandable portion is expanded in a manner so as to be sandwiched in a narrow space between a seat and a side surface portion of the vehicle, and the expansion of the expandable portion is limited by the seat and the side surface portion of the vehicle, and is not fully expanded, the tension force generated in the air belt becomes smaller than the tension force generated at a time when the expandable portion is fully expanded. Hitherto, even in such a case, actions such as raising the gas pressure generated by means of an inflator so that the necessary tension force is generated, increasing the length of the expandable portion, or the like is required. This necessitates complicated designing work.